Molecular Model of ZinconWilliam F. ColemanThe Featured Molecules this month are the tautomeric forms of the colorimetric reagent zincon, used in the paper by Maria Mar Areco, Maria dos Santos Afonso, and Erika Valdman on the bioabsorption of zinc, and by extension other metal ions, by seaweed. The structures presented have been calculated at the DFT/6-31G(d) level using the B3LYP functional. These structures represent energy minima, but not necessarily global minima. The structures could be used as an introduction to the concept of tautomerism, with students being asked to develop a definition of the term based on their observations of the difference(s) in linkage in the two forms. An intramolecular hydrogen bond is found in each structure, and introductory chemistry students could be encouraged to look for these structural features in molecules that are more complex than those typically encountered to introduce hydrogen bonding. More advanced students could use computational techniques to explore the energy differences between the two forms, and compare those differences to the ones observed between more traditional keto/enol examples.

Calorimetry / Thermochemistry |

Water / Water Chemistry |

Biological Cells

Molecular Models of Plant HormonesWilliam F. ColemanThe paper "Synthesis of Plant Auxin Derivatives and Their Effects on Ceratopteris richardii" by Corey E. Stilts and Roxanne Fisher describing an experiment begun in the organic labs and completed in a biochemistry cell biology lab provides the featured molecules for this month. The molecules in Figure 1 of that paper have been added to the collection. There is nothing particularly surprising about their structures, but students might be interested in seeing whether they can determine any structure/regulating effect relationships as the number of synthesized auxin derivatives grows. Additionally, students with little or no biochemistry background might wish to explore other systems that act as growth regulating hormones in plants, as an introduction to the variety of molecular structures that can display such bioactivity. Such molecules range from the very simple, ethene, to the adenine-derived cytokinins (an example of which, zealtin, is shown here) and the brassinosteroids. Brassinolide, a commonly occurring brassin, is also shown. These latter two structures have also been added to the molecule collection. All of the structures have been optimized at the HF/6-31G(d) level.